The major topic of developing an electrolytic capacitor is increasing the conductivity of the electrolyte to reduce the equivalent series resistance (ESR) and improve the reliability of a capacitor. A conductive polymer has a higher conductivity than that of a liquid state electrolyte or a solid state organic semiconductor complex salt (e.g. TCNQ composite salt) in a conventional electrolytic capacitor, and a suitable insulation property at high temperature, such that the conductive polymer is the most common solid state electrolyte utilized in a modern electrolytic capacitor.
Compared to a conventional liquid state electrolyte, a conductive conjugated polymer (formed by in-situ polymerization) used as an electrolyte in a capacitor may give the capacitor lower impedance and higher thermal stability. However, the withstanding voltage of the conductive conjugated polymer is dramatically lower than that of the liquid state electrolyte. As such, the low working voltage of the conductive conjugated polymer is the major obstacle in the applications for the electrolytic capacitor.
Accordingly, a novel capacitor structure is called for to overcome the limitations described above.